New Graphene Filter Could Remove Salt From Saltwater

Water covers 71 percent of the Earth's surface, and yet it can still be a scarce resource. That's because nearly all the Earth's water is held in the oceans, and it's incredibly difficult to purify that salt water to make it drinkable. Typical desalination works through flash heating or reverse osmosis, both of which require huge amounts of energy. This makes desalination impractical in remote areas or on a large scale.

Fortunately, a group of researchers from Shinshu University and Pennsylvania State University may have developed a better way to purify water. The group developed a type of molecular sieve using hybrid graphene oxide membranes to filter out the salt from saltwater more cheaply.

"Our dream is to create a smart membrane that combines high flow rates, high efficiency, long lifetime, self-healing and eliminates bio and inorganic fouling in order to provide clean water solutions for the many parts of the world where clean water is scarce," says study author Mauricio Terrones. "This work is taking us in that direction."

Using filters to remove contaminants from water is nothing new—the filter on your kitchen tap can remove hazardous chemicals—but salt is tricky to remove because salt ions are smaller than water molecules. An ordinary filter will let those smaller particles through, so the team had to develop a different kind of filter.

They turned to a graphene oxide membrane, which has previously shown promise as a salt filter. Graphene oxide is great at blocking salt ions while letting water through, but the challenge is building a membrane durable enough to survive for long periods of time. In particular, chlorine—a common water treatment chemical—rapidly degrades pure graphene oxide membranes, so the group wanted to find a better solution.

The scientists developed a kind of hybrid filter that incorporated pure graphene into the graphene oxide membrane to better resist the effects of chlorine. In addition, the membrane holds up better against strong water currents and can be manufactured much more cheaply than standard graphene oxide membranes.

The end result is a filter that can block 85 percent of salt molecules while still letting water through. This makes graphene oxide a real alternative to reverse osmosis or flash heating, and because graphene oxide doesn't require any electricity to run it may be much more efficient.

That's good news for the 20 percent of the Earth's population that doesn't have access to clean drinking water. This project is still in the early stages, but if the team can improve the amount of salt filtered by the membrane it could be used to bring clean water to millions of people around the world.

A Part of Hearst Digital Media
Popular Mechanics participates in various affiliate marketing programs, which means we may get paid commissions on editorially chosen products purchased through our links to retailer sites.